E=mc2. Energy equals mass times the speed of light squared. The original statement is: If a body gives off the energy L in the form of radiation, its mass diminishes by L/c2. Ist die Tragheit eines Korpers von Seinem Energieghalt Abhangig? 1905
Each ray of light moves in the coordinate system ‘at rest’ with the definite, constant velocity V independent of whether this ray of light is emitted by a body at rest or a body in motion.